Passive Exposure and Persistence of Gunshot Residue (GSR) on Bystanders to a Shooting: Comparison of Shooter and Bystander Exposure to GSR

Abstract

Gunshot residue (GSR) particles released from a firearm at the time it is discharged may be deposited onto nearby surfaces including the hands and clothing of the shooter and any bystanders. This study measured the relative amount of GSR detected on the shooter and on three bystanders in close proximity. Test-firings were conducted in duplicate using five different handguns with ammunition containing conventional lead, barium, and antimony based primers. Samples were collected from the right hand of the shooter 15 minutes after discharge. Bystanders were sampled 15 minutes after discharge and 2 hours after the initial sampling. A scanning electron microscope with an energy dispersive X-ray detector was used to analyze the samples. A high variability of GSR deposition was observed between firearm/ammunition combinations and between replicate firings. In some instances bystanders had similar concentrations of GSR on their hands to the shooter, making it impossible to distinguish between the two on the basis of particle numbers. Furthermore, after an additional 2 hours, most of the bystanders who initially had GSR particles on their hands had lost them through routine activity. The loss was comparable to what was expected from the hands of shooters based on information published in the literature. RésuméLes particules de résidus de tir dégagées lorsqu'une arme à feu est déchargée peuvent se déposer sur les surfaces à proximité, incluant les mains et les vêtements du tireur et des spectateurs. Cette étude mesurait la quantité relative de résidus de tir détectés sur le tireur et sur trois spectateurs à proximité. Les tirs d'essai ont été répétés utilisant cinq armes de poing avec des munitions à amorce conventionnelle de plomb, de baryum et d'antimoine. Des échantillons ont été recueillis sur la main droite du tireur 15 minutes après le déchargement. Des échantillons ont été recueillis sur les spectateurs 15 minutes après le déchargement, ainsi que deux heures après l'échantillonnage initial. Les échantillons ont été analysés à l'aide d'un microscope électronique à balayage couplé à un spectromètre à rayon X par dispersion en énergie. Une grande variabilité a été observée pour ce qui est du dépôt de résidus de tir entre différentes combinaisons d'armes à feu et de munitions, ainsi qu'entre les répétitions de tirs. Dans certains cas, les spectateurs avaient sur leurs mains des concentrations de résidus de tir similaires à celles recueillies sur le tireur, rendant impossible toute distinction entre les deux pour ce qui est du nombre de particules. De plus, après deux heures supplémentaires, la majorité des spectateurs qui, au Downloaded by [University of Otago] at 08:46 29 July 2015 90 départ, avaient des particules de résidus de tir sur leurs mains, les avaient perdues lors d'activités quotidiennes. La perte était comparable à celle attendue des mains du tireur, basée sur d'autres études publiées.

Distribution of gunshot residues – The influence of weapon type

“…The same, however, holds true for bystanders in the vicinity of several meters. Passive exposure would render these persons ''GSR positive'' [26].…”

“…[7,24,25]) on the distribution of GSR particles. Possible ambiguities in assigning the results of a GSR analysis to a specific shooting event have been reported [26]. In the light of these studies, a critical evaluation of GSR investigations as a means of evidence in court seems to be appropriate.…”

An experimental investigation of the indirect transfer and deposition of gunshot residue: Further studies carried out with SEM–EDX analysis

“…Rather, material can be acquired as a result of contact with a surface bearing GSR, or via proximity to a firearm discharge [5]. GSR may also be deposited on an individual who has entered a room in which a firearm was recently discharged [6,7].…”

Quantifying gunshot residues in cases of suicide: Implications for evaluation of suicides and criminal shootings

“…Although there is a significant body of knowledge in regards to transfer and persistence of GSR particles, especially primer derived particles( [5][6][7]), there are some substantial gaps, such as the quantity of deposition of GSR as a result of a single shot, and deposition from shotguns and 0.22 rimfire rifles, which are weapons that feature prominently in crime in Australia. One way of quantifying the transfer of GSR to the hands of a shooter, short of setting-up test firings involving a range of firearms and a range of calibres, is to measure deposition of particles on victims of firearm-related suicides.…”